GIANT CELL FIBROBLASTOMA
This is a rare but distinctive tumor that is found most commonly in infants and children. It shares immunocytochemical, cytogenetic, and behavioral features with dermatofibrosarcoma protuberans though the histology is not identical. There have been cases having features of both tumors either initially or in recurrences. This type of tumor can recur though none has been reported to metastasize.

The tumor is characteristically found in the subcutis, lower dermis, or in a combination of these loci. Regional variation in terms of cellularity and morphology is common. Highly cellular, often myxoid, primitive spindle cell-rich areas contrast with less cellular, more collagenized areas. Infiltration of the subcutis can have the same pattern as that found in dermatofibrosarcoma protuberans or in fibrous hamartoma of infancy. Sinusoidal, pseudovascular ('angiectoid') spaces are one of the defining features of this tumor, and giant cells may be found near the spaces or scattered in stroma elsewhere. The spindle cells are reported to be CD34 positive.


This case is from the chest of a young child.
 
 
Composite scan power view of the top part of the tumor. The horizontal slit (space) within the dermis near the top center is artifactual. The most cellular area is in the left side of the picture. Angiectoid spaces are best seen in the right side of the picture.
Low power view from the left side of the tumor. Primitive spindle cells are found in abundance. The stroma is slightly myxoid. Storiform figures were not found in this particular tumor.
Low power view from near the right side of the tumor. Pseudovascular (angiectoid) spaces are prominent, and they are somewhat sinusoidal in appearance.
Medium power view from another area. Connective tissue mucin may be absent or it may be present in varying degrees in the pseudovascular spaces. This is similar to the mucin that is sometimes found in pseudovascular spaces in nevocellular nevi. A few giant cells are near the lumen.
High power view from another area. Several giant cells are found in minimally cellular collagenous stroma.
Scan power view from deep within the tumor (deeper than depicted in the composite scan view). SM arrow points to skeletal muscle entrapped by the tumor. The pattern of infiltration of adipose tissue that is seen in this picture is a regular feature in dermatofibrosarcoma protuberans and can also be seen in fibrous hamartoma of infancy.

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